1. Field of the Invention
This invention relates to the use of chemical sorbents to reduce the levels of contaminants from waste streams. In particular, the invention relates to the use of used alumina, enriched with sulfur, to reduce or eliminate inorganic contaminants, including, but not limited to heavy metals or D-block metals, from waste streams. More particularly, the invention relates to the use of used alumina to reduce the levels of mercury and arsenic from waste streams.
2. Background of the Invention
Industrial pollutants such as heavy metals, D-block metals, mercury and arsenic pose significant health-related risks to the public. For example, several metal ions and transition metal ions have been associated with asthma symptoms such as activation of mast cells and enhanced allergen-mediated mast cell activation. Walczak-Crzewiecka, et al. “Environmentally Relevant Metal and Transition Metal Ions Enhance Fcε RI-Mediated Mast Cell Activation,” Env. Health Perspectives 111(5) (May 2003). Because these substances are generated as a by-product of industrial processes, it is important to find effective means to reduce their release into the environment.
For example, mercury emissions from coal-fired utilities, commercial boilers and solid waste incinerators represent a serious environmental problem and have been the focus of many regulatory deliberations. The Clean Air Act Amendments of 1990 (Tit. 1H, § 112(b)(1)) require major sources to use maximum available control technology to reduce mercury emissions. The United Nations has considered binding restrictions on the use of mercury through its environment program and has announced that it will begin to assist countries in developing methods for reducing mercury emissions. Lacey, M., “U.N. Conference Backs Efforts to Curb Mercury Pollution,” NY Times (Feb. 10, 2003). At present, coal-fired power plants emit the largest source of mercury emissions at 32.7%. Municipal waste incinerators and non-utility boilers each contribute approximately 18% of mercury emissions. Medical waste incinerators contribute 10% of mercury emissions.
Mercury exposure has been associated with neurological and developmental damage in humans. Developing fetuses and young children are at particular risk of the harmful effects of mercury exposure. In a report prepared for Congress, the Environmental Protection Agency (“EPA”) identified mercury as a particular danger to public health. Among other health-related concerns, the report identified increased levels of mercury in the blood of women of childbearing age. “Mercury Threat to Children Rising, Says an Unreleased EPA Report,” Wall St. J., Feb. 20, 2003, A1. Mercury contamination is also a concern for populations exposed to dental practices or dental waste, clinical chemistry laboratories, pathology laboratories, research laboratories, chlor-alkali facilities, and health care waste incinerators.
To address these concerns, the EPA proposed regulations that would require reductions in mercury emissions from coal-fired power plants. EPA Press Release, Dec. 14, 2000. In addition, legislation has been proposed that would cut mercury emissions by 50% by 2010 and by 70% by 2018. Wall St. J., Feb. 20, 2003. However, despite the desire to reduce mercury emissions, presently there are no commercially available technologies to control mercury emissions. Id.
Similarly, exposure to arsenic poses potentially significant health risks. Arsenic is a natural element, distributed throughout the soil and in many kinds of rock. Because of its ubiquitous presence, arsenic is found in minerals and ores that contain metals used for industrial processes. When these metals are mined or heated in smelters, the arsenic is released into the environment as a fine dust. Arsenic may also enter the environment from coal-fired power plants and incinerators because coal and waste products contain some arsenic. Once arsenic enters the environment, it cannot be destroyed.
Arsenic exposure causes gastrointestinal problems, such as stomach ache, nausea, vomiting, and diarrhea. Arsenic exposure can also yield decreased production of red and white blood cells, skin changes that may result in skin cancer, and irritated lungs. Inorganic arsenic has been linked to several types of cancer and is classified as a Group A, human carcinogen. In high amounts (above about 60,000 ppb in food or water), arsenic may be fatal. Because of the serious adverse health effects related to arsenic, in 2001, the EPA issued regulations limiting the amount of arsenic in drinking water to 10 parts per billion. 66 Federal Register 6976.
Similar adverse effects have been associated with other inorganic contaminants such as cadmium, chromium, lead, and selenium. Cadmium, for example, is associated with chronic kidney, liver, bone and blood damage. Like mercury and arsenic, cadmium occurs naturally in metal ores and fossil fuels; industrial releases of cadmium are due to waste streams and leaching of landfills. Another contaminant, chromium, is associated with such long-term effects as damage to liver, kidney, circulatory and nerve tissues, as well as skin irritation. The level of chromium in drinking water is regulated by the Safe Drinking Water Act of 1974. Chromium is released to the environment through chemical manufacturing and combustion of natural gas, oil, and coal. Lead is another contaminant associated with negative health effects, such as brain and nerve damage in children, behavior and learning problems, and reproductive problems. Lead is released to the environment through various industrial processes.
Various carbon-based sorbents have been identified for removing mercury vapor from gas streams. T. R. Carey and C. F. Richardson, “Assessing Sorbent Injection Mercury Control Effectiveness in Flue Gas Streams,” Environmental Progress 19(3):167-174 (Fall 2000). For example, Selexsorb® HG (Alcoa World Alumina, LLC, Pittsburgh, Pa.) and Mersorb® (Nucon International, Inc., Columbus, Ohio) are commercially available carbon-based mercury sorbents. Recycled tires have also been identified as a source of activated carbon that could be used for mercury removal. C. Lehmann et al., “Recycling Waste Tires for Air-Quality Control,” January 2000. Activated carbon has many drawbacks for use in large-scale industrial processes, however. In particular, commercially available activated carbon is a relatively expensive sorbent. Although transformation of waste tires into activated carbon is an environmentally friendly means of recycling harmful waste, it is a complicated, lengthy, energy-intensive and time-consuming process. Additionally, the yield of activated carbon from waste tires is relatively low.
Thus, there is a need for new technologies to efficiently and cost-effectively reduce the level of inorganic contaminants, such as mercury and arsenic for example, in industrial emissions.
Activated alumina is a well-known sorbent. Industrial applications for activated alumina include: natural gas processing, dryers and forming, ethylene processing, petroleum refining, air separation, catalyst support, hydrogen peroxide manufacturing, and water treatment. Alumina has applications in ceramics, refractories, refining, abrasive materials, glass, cements and powder metallurgy, electrical applications, coatings, fibers, metallizing, and gas dehydration.
As used herein, “used alumina” is a by-product of a chemical or industrial process that enriches the alumina with sulfur or sulfur-containing compounds. A significant source of used alumina is the Claus process, which is used to recover elemental sulfur from hydrogen sulfide in gases. Industrial applications of the Claus process include, without limitation, steel production, oil refineries and natural gas refineries. Activated alumina is used as a catalyst in the Claus process. As more sulfur is deposited onto the activated alumina through the Claus process, the material loses its catalytic ability and becomes “spent” or “used.”
Used alumina represents a significant source of industrial waste. Approximately 50,000 to 75,000 tons of used alumina are generated annually. Regeneration of used alumina, such as Claus catalyst is an expensive process, however. Because it is economically disadvantageous to regenerate the used alumina, much of the used alumina ends up in landfills. Thus, there also exists a need to recycle used alumina into other useful applications.